This invention relates to a low-pass filter of the coaxial cable type comprising several layers, produced by cable-manufacturing techniques and using a long, distributed capacitance "filter-line" which, when cut into pieces, produces lumped lossy filters.
The difficulties of the brute force low pass filter to suppress interference in electrical power circuits are well known. Essentially, such filters use reactive elements which do not destroy the parasitic energy but only switch or convey it to ground, with more or less success.
The efficiency of the "absorption" principle, which dissipates stopband energy in the form of heat inside the filter, is well known from U.S. Pat. Nos. 3,191,132 and 3,309,633, and this principle has been studied and adopted by a number of companies. Lossy lines are now universally accepted for high performance car ignition cables. Lossy filters exist, with various approaches to introduce absorption in or between the reactive components of the filter. In the inductive components such approaches include direct magnetic losses through special magnetic materials, synthesized magnetic losses, and conductive losses through artificial skin effects (see U.S. Pat. No. 3,573,676). In the capacitive components such approaches include dielectric losses through special dielectric materials, and synthesized dielectric losses by diffusion, by semiconductive materials, by mixtures, etc. As between inductive and capacitive components such approaches include interface losses through multiple reflections or pseudoresonances (see French Pat. No. 1.479.228). All of these effects can be used alone or together, and embody an "integrated" concept of lossy filters.